Heretofore, as an I/Q orthogonal signal generator used for an image rejection mixer (IRM) or a vector sum phase shifter, there has been known a polyphase filter. The polyphase filter, which includes resistors and capacitors, has a function of generating I/Q orthogonal signals inside the vector sum phase shifter, and is required to have a low insertion loss, and high amplitude accuracy and phase accuracy. In general, in order to improve the phase accuracy, a method of using a polyphase filter having a multi-stage configuration is adopted, but the method has a problem of an increased insertion loss.
As such polyphase filter, there has been proposed an amplitude matching type polyphase filter, which is configured to set resistance values and capacitance values so as to correct an amplitude error to be output. Further, there has been proposed a polyphase filter in which an amplitude matching type polyphase filter and a multi-stage polyphase filter are combined to achieve amplitude matching and phase matching (see Patent Literature 1, for example).
Moreover, in order to improve the phase accuracy without using the polyphase filter having the multi-stage configuration, there has been proposed a polyphase filter that uses varactors, which are variable capacitors, as capacitors to achieve high phase accuracy (see Non Patent Literature 1, for example).